Rolled passive reflective antenna tending to unroll under bias of entrapped air



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Jan. 12, 1965 3,165,751

T. CLARK ROLLED PASSIVE REFLECTIVE ANTENNA TENDING TO UNROLL UNDER BIAS OF ENTRAPPED AIR Filed Oct. 26, 1962 INVENTOR Trevor Clork BY iw.; .5m

ATTORNEY WITNESSESI United States Patent() Pennsylvania Filed Oct. 26, 1962, Ser. No. 233,293 2 Claims. (Cl. 343-915) The present invention relates to radio antennas and more particularly to a passive reflective foldable antenna that may be unfolded to be erected and orbited in space.

Reflective antennas orbiting in space are useful for extending the transmission of short wavelength radiations and microwave radio communications to points all around the earth as is well known to those skilled in the art. The so-called Echo Satellite is a balloon with a rellective surface for electromagnetic radiations that has been orbited in spaced andinilated. However, for various reasons, the balloon gradually is losing its spherical shape and has become wrinkled so that it is less efficient and effective as a reflector for electromagnetic radiations. Another form of passive reflector for electromagnetic radiations was attempted to be obtained by ejecting into space a cloud of metallic filaments called needles which were intended to function as reflective dipoles for a band of frequencies of electromagnetic radiations. This form of antenna has thus far failed to be achieved in, that the needles apparently dispersed and were lost in space.

It is a principal object of the present invention to provide an improved form of foldable wide banddipole passive reflective antenna that may bek easily unfolded to be erected after being orbited in space and that will retain its reflective effectiveness as a communications satellite indenitely.

Another object of the invention is to provide a simplified form of omnidirectional and broadV band dipole passive reflective antenna that may be easily erected and randomly oriented in space and which will function effectively without critically as to its position and attitude rela tive to the radiation to be reflected.

A st-ill further object of the invention is to provide,

an improved form of orbiting passive reflective antenna that is substantially immune to damage from micrometeorites and particles in space and that is not deleteriously affected by varying exposure to heat and light rays from the sun and to other objects in space.

According to the invention, a relatively large thin panel of electrically insulative and foldable sheet material is arranged to be folded in the nose cone of a rocket from which it may lbe ejected to orbit in space and unfolded. The foldable panel may be provided with suitable means to assure the unfolding of the panel in space when it is ejected. For example, longitudinal hollow ribs may be provided on the panel to contain atmosphere, a gas under pressure, or a coiled or rolled spring to unfold the panel when ejected into space. At least one planar surface of the panel is provided with a large plurality of randomly oriented metallic elements secured thereto such as, -for example, filaments of aluminum or similar high conductivity metal having a length equal to one half the wavelength of the electromagnetic radiation to be reflected.

If a specified band of frequencies of electromagnetic radiations is to be reflected, then the randomly oriented metallic filaments may be of variousdifferent individual lengths varying from a minimum length to a maximum length corresponding to the minimum and maximum wavelengths of energy to be reflected. Thus, such random oriented filaments may function as an omnidirectional broad band reflective antenna with substantially no particular polarization relative to received energy to be reflected. It should be borne in mind that the thin sheet of insulating material forming the panel for supporting and fixing the metallic filaments in random orientation to each other in accordance with the invention, is itself essentially transparent to the electromagnetic radiations and hence there is no need to orient or stabilize the position of the reflector panel in space since the dipoles will re-radiate in all directionsalmost as does the re-radiating sphere of the so-called Echo Bal-v loon type.

Further objects, features and the attending advantages of the invention will ybe apparentwith reference to the;

following specification and drawing, in which:

FIGURE l is a fragmentary perspective elevational view of the passive reflective antenna of the invention in the unfolded state; FIG. 2 is an enlarged fragmentary detail perspective of a portion of the panel of FIGURE l showing one ar-v rangement of randomly oriented metallic reflecting elements on its planar surface;

FIG. 3 is an elevational view of the reflective panelV of FIGURE l as it may be partially rolled for stowage in a missile nose cone or the like;

FIG. 4 is a detailed fragmentary perspective view partly, broken away toshow a modified form of panel unfoldn ing means;

FIG. 5 is an enlarged fragmentary sectional view of a modified form of reflective panel;

FIG. 6 is an enlarged fragmentary sectional View of yet another modied form of reflective panel of the invention.

Referring now to FIGS. 1-3 of the drawing,V .onev

tions as a reflective dipole. If the electromagnetic energyV to be reflected is a band of wavelengths having lower and upper limits, then individual ones of the metallic fila` ments 11 would be cut to individually different lengthsvaryingfrom Vthe minimum length corresponding to one half wavelength of the minimum wavelength of energy to be reflected to a maximum length corresponding to' `one half -wavelength of the maximum wavelength of electromagnetic energy to be reflected.

As shown by the enlarged view Vof FIGURE 2 of thel drawing, each of the metallic filaments 11 is randomlyV `positioned on the electrically insulative supporting sheet or panel 10. The random positioning may be in reference both to the position'of orientation and the occurrence of varying lengths of the individual filaments which may also v be randomly occurring'in -Variouspositions on the sup'y porting panel 1li. For example, each of various lengths i f 'of the metallic filaments 11 may be all secured irr they',

same plane as the planar surface'of the supporting sheet 1l). On the other hand, each of the metallic filaments 11 i may be secured to the planar surface of the supportingV sheet 10 at varying angles to the plane of the supporting sheet and to each other. It should be apparent that,v re'- gardless of the angular position or orientation of individual ones of the metallic filaments 11 on the planar surface of the supporting sheet 10, there will be no particular polarization emphasis for the reflective nature of the antenna comprising the plurality of random oriented iila- Patenteddan. 12, 1965 i 9 nents. This will be understood when it is borne in mind :hat the electrically insulative sheet of thin material is :afectively transparent to the electromagnetic radiations to Je re-radiated by the various randomly disposed metallic iipole elements 11.

Each of the metallic elements 11 may be secured in ranlom position relative to each other on the electrically in- ;ulative supporting sheet 10 by any suitable means. For axample, a layer of adhesive material 12 may be secured o a surface of the supporting sheet 10 and the metallic ieedle elements 11 may be simply sown onto the adhesive ayer much in the manner of sowing grain. If a particuar sensitivity toward a desired range of frequencies for the :lectromagnetic radiations to be re-radiated is desired, it vould be preferable to remove any of the electrical elenents 11 that are physically contacting other metallic elenents in a manner to alter the effective dipole length of `uch metallic elements. However, depending upon the :fiiciency desired, it is not in all cases necessary to pre- `erve a complete electrical independence for each of the netallic elements 11. Also, although the metallic elenents 11 are shown to be secured to one side only of the .upporting sheet 10, it is within the purview of the invenion to also secure additional refiective elements 11 to the )ther side of the supporting planar sheet 10.

The adhesive material may, in similar manner, be apxlied to the dipole elements themselves at the time they tre ready for attachment to the supporting sheet. Note hat the adhesive material should not volatilize when in space. For this reason, a thermo-setting resin might be nost suitable. Another method would utilize a thermo- )lastic resin as the supporting sheet material. The needles :ould be sown onto the sheet when warm and molten. lpon cooling the dipole needles will be found to adhere n'operly to the sheet.

The planar sheet 10 with metallic dipole elements se- :ured thereon may be rolled up into a cylinder for inser- :ion into a missile nose cone or the like as shown by ?IGURE 3 of the drawing. The cylinder may then be folded, rolled or coiled. When the supporting sheet panel l0, as rolled up and carried in a nose cone, is ejected into :pace, it may be easily unfolded or unrolled to present a arge area of captive metallic dipole elements within range )f earthbound radio transmitting and receiving stations. In orler to facilitate the unrolling and erection of the reiective panel in space one or more longitudinal ribs 15 nay be formed in the panel or secured to the panel. fhese ribs may be formed of material that is impervious o gas or atmosphere and may be sealed at one end as ;hown by 16 of FIGURE 3. If the panel is rolled into :ylindrical form in the atmosphere a certain amount of he atmosphere will be trapped within the hollow rib 15, md when the rolled panel is ejected into space, the enrapped atmosphere in the rib 15 will have sufhcient pres- `ure relative to the near vacuum of space to expand the 'ib 15 and unroll the panel as will be obvious to those `killed in the art. It will not be necessary to seal both nds of the rib 15 since once the panel is erected it will etain its unfolded and erected state in space indefinitely. t should be pointed out that for the purposes of this in- 'ention, the sheet need not be completely fiat. Unrolling s required only to present the greatest reiiective surface ,rea which is reasonably possible. Alternatively, a source f gas under pressure (not shown) may be connected to he erecting rib 15 at the time of ejection of the panel nto space.

Yet another manner of facilitating the unfolding and rection of the passive reflective panel in space would be o enclose a longitudinal coil spring Ztl such as shown by iIGURE 4 of the drawing within the longitudinal tube Ir rib 15. Alternatively, the longitudinal coil spring Ztl nay be secured to the panel 10 at individual points along ts length instead of enclosing it within a tube or rib strucure 15. Various modifications of such arrangements will le obvious to those skilled in the art.

If desired the supporting panel of flexible sheet material may be a fabric comprised of warp and Woof yarns 30, 31 of electrically insulative material as shown by FIG- URES 5 and 6 of the drawing. A plurality of randomly disposed metallic filaments such as shown for example at E2-34- may be secured to extend generally perpendicularly from one surface of the fabric panel (FIGURE 5 alternatively, the filaments such as shown by 35 and 36 of FIGURE 6 of the drawing may extend generally perpendicularly from opposite sides of the fabric panel respectively. Alternatively, the filaments may be randomly disposed within the plane of the fabric panel. It will be noted from the enlarged detail of both FIGURES 5 and 6 of the drawing that each of the respective metallic filaments 32-36 may be of different lengths randomly positioned relative to each other. That is to say, no particular pattern of varying lengths of one filament adjacent another lament is to be observed. The random orientations of the reflecting metallic dipole elements as used with any of the forms of the invention assures that the reective characteristics of the antenna will be substantially omnidirectional and non-polarized over its entire bandwidth. The provision of the flexible support sheet or fabric of insulating material to which the metallic refleeting dipole elements are secured and fixed in randomly oriented positions and sizes assures that such aggregation of refiective needles will not be dispersed relative to each other in space. The panel can be made quite large in area and can be easily foldable to a small compact form for insertion in a missile nose cone. After the panel has been unfolded and erected in space it will retain its shape indefinitely since it will not be affected by punctures when micrometeorite particles or the like pass through the fabric or supporting sheet. The vast numbers of reflective metallic filaments that may be supported on a large area of flexible support sheet or fabric will assure that the efficiency and effectiveness of the reflective antenna will be maintained notwithstanding occasional punctures of the panel of supporting material by the micro-meteorite particles. In addition, since the exact shape of the supporting panel as unfolded in space is not critical to the functioning of the individually supported and randomly posi-4 tioned and oriented dipole reflective elements, any changes in attitude or surface shape of the supporting panel during its orbiting period in space lwill not seriously reduce the efiiciency and effectiveness of the antenna.

Although many variational embodiments of the invention will be apparent to those skilled in the art, a specific example of the invention might comprise a plastic film panel having an adhesive surface to which are bonded a plurality of aluminum filaments varying in diameter from a diameter of one thousandth to one ten thousandth of an inch and having a length of approximately 1.5 centimeters so as to be resonant to a microwave radio signal of about 1000 megacycles. Obviously the various different lengths for the metallic filaments may be greater than or less than 1.5 centimeters depending on the center frequency and the bandwidth of the electromagnetic radiations to be reflected.

I claim as my invention:

1. A passive refiective antenna to be orbited Vin space comprising, a panel of electrically insulative foldable sheet material adapted to be folded and stored within a space capsule under atmosphericv air conditions and ejected from the capsule into space, at least one tubular rib of material impervious to atmosphere secured to and extending along said panel in a direction for erection of the panel in space, a plurality of metallic filaments supported in random positions from a surface of said material, each of said metallic laments having a length corresponding to one half the wavelength of the desired frequency of electromagnetic radiation to be reflected to thus function as a reflective antenna for such radiation, and said tubular rib entrapping ambient air while said panel is folded under atmospheric air conditions whereby when a folded panel is ejected from the capsule into the near vacuum of space the panel is unfolded to a variable extent to form an enlarged area of reflective antenna with no predetermined geometric configuration.

2. A passive reflective antenna to be orbted in space comprising, a panel of electrically insulative -foldable sheet material adapted to be folded and stored within a space capsule under atmospheric air conditions and ejected from the capsule into space, at least one tubular rib of material impervious to atmosphere secured to and extending along said panel in a direction for erection of the panel in space, a plurality of metallic lilaments of different lengths supported in random positions from a surface of said man broad band reflective antenna for such radiation, and said tubular rip entrapping ambient air while said panel is folded under atmospheric air conditions whereby when a folded panel is ejected from the capsule into the near vacuum of space the panel is unfolded to a variable extent to form an enlarged area of reflective antenna with no predetermined geometric configuration.

References Cited in the file of this patent UNITED STATES PATENTS 2,055,862 Friedman Sept. 29, 1936 2,212,128 Richter Aug. k20, 1940 2,752,594 Link et al June 26, 1956 3,047,860 Swallow et al. July 3l, 1962 OTHER REFERENCES Lafond: Paraballoon Antennas, New Space Tool, Missiles andV Rockets, pages 21-25, January 11, 1960. 

1. A PASSIVE REFLECTIVE ANTENNA TO BE ORBITED IN SPACE COMPRISING, A PANEL OF ELECTRICALLY INSULATIVE FOLDABLE SHEET MATERIAL ADAPTED TO BE FOLDED AND STORED WITHIN A SPACE CAPSULE UNDER ATMOSPHERIC AIR CONDITIONS AND EJECTED FROM THE CAPSULE INTO SPACE, AT LEAST ONE TUBULAR RIB OF MATERIAL IMPERVIOUS TO ATMOSPHERE SECURED TO AND EXTENDING ALONG SAID PANEL IN A DIRECTION FOR ERECTION OF THE PANEL IN SPACE, A PLURALIT OF METALLIC FILAMENTS SUPPORTED IN RANDOM POSITION FROM A SURFACE OF SAID MATERIAL, EACH OF SAID METALLIC FILAMENTS HAVING A LENGTH CORRESPONDING TO ONE HALF THE WAVELENGTH OF THE DESIRED FREQUENCY OF ELECTROMAGNETIC RADIATION TO BE REFLECTED TO THUS FUNCTION AS A REFLECTIVE ANTENNA FOR SUCH RADIATION, AND SAID TUBULAR RIB ENTRAP- 